A choking question, really!

[hilldweller]

Hi all,
I have read a lot of tube amp books and the more I read, the more confounded I get. So many people with so many takes on any given subject, It tends to get mind boggling.
My question here has to do with power supply chokes, In a book I read: http://www.amazon.com/Build-Your-Audio- ... amplifiers

All of the projects there use 10 h chokes in their power supplies. Others use 1 h, What are the advantages of either? 10h costs buku bucks, others, not so much. I understand that clean DC is a plus.

[Geek]

Morgan Jones has a really simple rule of thumb that by my bench tests, is accurate:

Minimum inductance in H = V/Ima

So a typical ST-70 gets say 430V and draws about 200mA at idle, so 430/200 = 2.15H, which is close to the original C354.

Personally I use the rule of thumb, then add 50% and use the closest inductance for the current I need to that figure.

With preamps and other real low current draw things, you're going to get unreasonably high inductances. So, what do you do? I use a higher voltage transformer and go C-R-C or just make a quick-and-dirty-MOSFET-and-zener regulator.

Cheers!

[DeathRex]

Someone somewhere decided 10H is a standard, and the audiophiles all followed. I must have 20 chokes and none are 10H, because they are expensive and big at the higher currents. I always go by 2 X 3.14 X 60 X H for the resistance I'll get for a choke. So if for a amp that draws 350ma, I have a 0.85H choke; 2 X 3.14 X 60 X 0.85 = 320 ohms @ 60 Hz and 25 ohms DC and makes very little heat for $6. A 320 ohm resistor at 350ma will drop 112 volts DC and put out 39.2 watts of heat.

I have that book too, never made one of his amps. Some of the schematics are drawn incorrectly (page 147), and some of his power supplies are over-engineered. Look at page 132, and contrast it with the B+ supply on page 142. He also really likes the EF86 (another of "If you use a pentode it has to be a EF86") bah try a 6EJ7. It is a simpler book to read, at least for me, than Morgan Jones, but for schematics, I would stick with Shannon's, JL labs other schematics found here or at DiyAudio.

[hilldweller]

Thanks Geek and DeathRex! I appreciate your knowledge

[battradio]

When copper was cheap and capacitors where expensive a 10 henry choke make a lot of sense , now days a 100 /100 uf cap at 500 volts is less than $15 the same amount of filtering is much cheaper with a small choke .

[kheper]

Hi all,
All of the projects there use 10 h chokes in their power supplies. Others use 1 h, What are the advantages of either? 10h costs buku bucks, others, not so much. I understand that clean DC is a plus.

higher inductance = less ripple voltage = less distortion

10H@300ma chokes weigh about 8-10lbs. They'll put a nice bend in your chassis (and a crimp in your wallet).

More recent theory is to use two smaller chokes than one large one: C-L-C-L-C. Two chokes are less prone to saturation than one (given the same current capacity), so maybe the theory is sound.

Depending on the chassis, you should be able to fit 2 Hammond 194Gs into it. 2 x 3H@250ma may produce less ripple than 1 x 10H@250ma.

http://www.hammondmfg.com/pdf/EDB194G.pdf

[hilldweller]

Thank you!
I have decided to go with these from Edcor. They tell me they are rated for 1kv
http://www.edcorusa.com/p/777/xc87-2h-300ma